The present invention relates generally to rotor windings for dynamoelectric machines and particularly to improvements in the rate of heat transfer within radial ducts through stacked rotor turns to cool the windings.
As will be appreciated by those practiced in the art of dynamoelectric machine design, the capacity of current machines is constrained by physical size considerations which are to be minimized to reduce cost. Further, resistive losses within the rotor windings generate heat which must be dissipated in order to avoid electromechanical failure. This poses a serious constraint on the capacity of a machine of given physical dimension. The high thermoconductivity of gaseous hydrogen, in conjunction with diagonal flow cooling arrangements, have been successfully exploited to increase cooling capacity within the constraints of the physical size of the machine and its thermal loading. Hydrogen cooling, however, causes additional cost and complexity. It has become increasingly apparent that additional means must be provided to manage the increase in thermal loading that- accompanies continuing efforts to coax additional electrical capacity from machines of a given physical dimension.
In U.S. Pat. No. 1,985,040, ducting is disclosed for flowing cooling air from the subslots of a rotor of a dynamoelectric machine to create a radial cooling flow through the ducts in direct contact with windings prior to exiting at the rotor periphery. This has become a common cooling practice, for example, see also U.S. Pat. No. 4,709,177, and it will be appreciated that this flow is turbulent in the fluid dynamic sense. The present invention extends the prior art cooling through the application of turbulators to each of the turns comprising each radial flow duct in order to enhance the mean level of turbulence and to proportionally enhance heat transfer. While turbulators have heretofore been employed to increase cooling rates within the interior flow passages of aircraft jet engine turbine blades, the application of turbulators to enhance fluid flow in the cooling system for rotors of dynamoelectric machines has not heretofore been accomplished.
In accordance with the present invention, a plurality of protuberances or turbulators, i.e., ribs or trips, are disposed in the radial flow cooling ducts of stacked rotor turns. The primary function of the turbulators is to increase turbulent fluid dynamic mixing between heated fluid adjacent to the duct wall and relatively cooler fluid near the duct centerline. This enhanced level of mixing brings cooler fluid in contact with the duct wall, creating greater potential for heat transfer. The turbulated ducts also increase the surface area exposed to the convective cooling gas. Areas within the ducts affording local fluid dynamic separation and reattachment for local enhancement of heat transfer are also created in the vicinity of the turbulators. The turbulators hereof are readily formed, for example, by coining the turbulators into the punched opening of each turn of the coil. The turns, of course, are stacked with radially spaced insulation strips interposed between adjacent turns. The turbulated openings through the stacked turns and the openings through the interposed insulation strips register with one another and form radial flow cooling passages or ducts extending from the rotor subslot radially outwardly to the air gap between the retaining wedges and the outermost turn and associated insulating strip. Various arrangements of the turbulators within the radial duct for optimal thermal performance may be provided, for example, by forming the turbulators along one side of the turns, alternating the turbulators on opposite sides of the duct, or forming dual turbulators on each turn within the duct.
Thus, increased rates of heat removal from the field windings of the rotor of large-capacity direct cooled electrical turbo alternators is afforded by the present invention. Additionally, rotors may be rewound or replacement rotors provided with the turbulated ducts for uprating the output or reactive capability of existing generator equipment. Importantly, no new components are introduced into the generator as a result of the enhanced cooling capacity provided by the present invention. Additionally, the present invention can be applied using any gaseous or liquid cooling medium (fluid).
Consequently, the invention enables an increase in the ampere-turn capability of turbo alternators of given physical dimension, resulting in a reduction in production costs per MW of output. Alternatively, the invention enables a reduction in the physical dimensions of machines of a given rating, which likewise results in a cost savings. Further, the invention enables a reduction of parasitic cooling flow pumping loss and windage, resulting in an improvement in overall efficiency and a reduction in perceived noise level. The invention also requires only a machining operation to extant rotor winding turns and therefore requires the addition of no new components for upgrading cooling capacity. The invention also has immediate application to a large class of dynamoelectric machines which employ the gaseous flow of air or hydrogen in direct cooling schemes, as well as to other heat transfer media, such as helium or water. Further, a particular advantage of the present invention is that it provides a completely passive heat transfer augmentation, requiring no chemical additives, acoustical input or other active stimuli. Further, the turbulators are readily manufactured through a simple single-stroke coining operation on new or existing field conductor turns or as a second stage of a progressive die punching operation. It does not require precise tolerances in order for the turbulators to perform their intended function.
In a preferred embodiment according to the present invention, there are provided rotor windings for a dynamoelectric machine comprising a plurality of stacked rotor turns, wall surfaces of each stacked rotor turn defining an opening in communication with a registering opening of an adjacent turn for flowing a fluid through the openings in communication with one another and a protuberance carried by a wall surface of at least one rotor turn projecting from the wall surface into the opening affording a turbulent flow of the fluid through the opening of the one rotor turn for positively mixing fluid in the opening adjacent the wall surface and fluid adjacent a central portion of the opening.
In a further preferred embodiment according to the present invention, there is provided a dynamoelectric machine comprising a rotor having a plurality of generally radially extending slots circumferentially spaced from one another, windings for the machine including a plurality of stacked rotor turns in each of the slots, means the stacked for introducing a cooling medium adjacent radially inner portions of rotor turn having an opening in communication with a registering opening of an adjacent turn for flowing the cooling medium from the introducing means through the registering openings in a radially outward direction, a protuberance carried by at least one rotor turn projecting into the opening affording a turbulent flow of the cooling medium through the opening of the one rotor turn for positively mixing cooling medium in the opening adjacent the wall surface and cooling medium adjacent a central portion of the opening.
In a still further preferred embodiment according to the present invention, there is provided a method of forming rotor windings for a dynamoelectric machine comprising the steps of punching a through opening in each turn of the rotor windings, coining the turn to form a protuberance in each turn projecting into the punched opening and stacking the turns in a rotor slot of the rotor of the dynamoelectric machine with the openings in registration with one another to form a flow passage.
In a still further preferred embodiment according to the present invention, there is provided a method of cooling the windings of a rotor in a dynamoelectric machine comprising the step of flowing a cooling medium generally radially outwardly through registering openings in stacked rotor turns having turbulators affording turbulent flow of the cooling medium therethrough for mixing cooling medium adjacent wall surfaces of the openings with cooling medium flowing along central portions of the openings.
Accordingly, it is a primary object of the present invention to provide enhanced cooling capacity in dynamoelectric machines affording a significant reduction in the temperature drop between the conductor turns and the cooling medium temperature for a given expenditure in parasitic cooling flow pumping loss, greater output for a given physical dimension of the machine, or alternatively a reduction in parasitic cooling flow pumping loss and windage, resulting in an increase in efficiency, a reduction in noise for a given rating and physical dimension and increased machine output for a given machine size without the added complexity of hydrogen cooling.